The objective of this research project is to define possible controls for DNA biosynthesis during normal and abnormal growth. The interactions of enzymatic and nonenzymatic factors in the initiation and elongation steps of DNA replication will be studied. A Mr 600,000 subspecies of DNA polymerase (pol alpha2) from HeLa cells has been purified to electrophoretic homogeneity and resolved into its subunit structure. The enzyme has associated primase (Mr 70,000), 5' to 3' and 3' to 5' exonuclease (Mr 69,000), diadenosine 5',5'''-P1,P4 tetraphosphate (Ap4A) binding (Mr 92,000) and DNA polymerase-alpha (Mr 145,000) activities. In addition, two associated accessory proteins, Cl (Mr 96,000) and C2 (Mr 52,000), function as primer recognition proteins for synthesis with primed single-stranded DNA templates. The interaction of DNA polymerase-alpha2 with other enzymatic and nonenzymatic proteins in DNA synthesis with defined DNA templates will be studied.